A master swordsman, Ruka is the former captain of the fencing team and a former member of the Student Council. His cunning, manipulative behavior belies a hidden desperation to live, and his influence on Juri becomes one of the major turning points for her character.

In the manga, Anthy served as Ruka's Rose Bride on several occasions before he left the school due to an unknown illness. He reappears at the school after a prolonged absence, claiming that he has recovered, though still not well enough to duel. He pushes Juri to duel Utena once again, but she throws the match after overhearing what she thinks is Ruka discussing with Touga how he's manipulating her. When she refuses to duel, Ruka himself is forced to duel Utena, and the strain causes a relapse of his illness. As he lies on the dueling field, he confesses to Juri that he pushed her because he thought she was the one worthy of Dios's power. Touga comments that Juri was in love with Ruka first, but when he left she switched her love to Touga. Ruka explains that he left Juri without saying goodbye to avoid the painful farewell.

In the anime, it is not clear whether or not Ruka was a Duelist before he returns. When he returns, he takes Shiori as his girlfriend, though it's made clear that he was simply manipulating her. He duels Utena once with Shiori as his Rose Bride and loses. He then dumps Shiori and begins to court Juri. From him we learn that it was Juri who told him, "If you believe in miracles, they will occur." Ruka says he is in love with Juri, and forcefully kisses her during a fencing match; he states that he believes she was in love with him before he disappeared. As in the manga, it is due to his feelings for her that he wants her to claim the power of Dios and defeat Utena in order to save her from her burdens. Juri denies she was ever in love with him. Ruka subsequently appears as Juri's Rose Bride in her final duel, after which he leaves the school. It's implied that Ruka died since the Shadow Girls report his death and he is not shown after his duel with Utena, but his ultimate fate still remains unknown.